Re: [PATCH v8 4/6] mm: mlock: Add mlock flags to enable VM_LOCKONFAULT usage

From: Michal Hocko
Date: Fri Aug 28 2015 - 10:32:57 EST

On Fri 28-08-15 16:31:30, Michal Hocko wrote:
> On Wed 26-08-15 14:24:23, Eric B Munson wrote:
> > The previous patch introduced a flag that specified pages in a VMA
> > should be placed on the unevictable LRU, but they should not be made
> > present when the area is created. This patch adds the ability to set
> > this state via the new mlock system calls.
> >
> > We add MLOCK_ONFAULT for mlock2 and MCL_ONFAULT for mlockall.
> > MLOCK_ONFAULT will set the VM_LOCKONFAULT modifier for VM_LOCKED.
> > MCL_ONFAULT should be used as a modifier to the two other mlockall
> > flags. When used with MCL_CURRENT, all current mappings will be marked
> > with VM_LOCKED | VM_LOCKONFAULT. When used with MCL_FUTURE, the
> > mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT. When used
> > with both MCL_CURRENT and MCL_FUTURE, all current mappings and
> > mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT.
> >
> > Prior to this patch, mlockall() will unconditionally clear the
> > mm->def_flags any time it is called without MCL_FUTURE. This behavior
> > is maintained after adding MCL_ONFAULT. If a call to
> > mlockall(MCL_FUTURE) is followed by mlockall(MCL_CURRENT), the
> > mm->def_flags will be cleared and new VMAs will be unlocked. This
> > remains true with or without MCL_ONFAULT in either mlockall()
> > invocation.

Btw. I think we really want a man page for this new mlock call.
Michal Hocko
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